1. Field of the invention
The present invention relates to an electroluminescence (EL) device having an emitting layer made of an emitting substance, which utilizes an electroluminescence phenomenon that is the emission of light resulting from application of an electric field to the substance. More particularly, it is concerned with an organic EL device in which the emitting layer is made of an organic luminous substance.
2. Description of the prior art
As organic EL devices, there have been known a device of two-layer structure type having two layers made of organic compounds respectively as shown in FIG. 1, in which an organic fluorescent thin film 3 (hereinafter referred as "emitting layer") and an organic positive-hole transport layer 4 are laminated with each other and are arranged between a metal cathode 1 and a transparent anode 2. There have been also known a device of three layer structure type having three layers made of organic compounds respectively as shown in FIG. 2, in which an organic electron transport layer 5, an emitting layer 3 and an organic hole transport layer 4 are laminated in sequence and are sandwiched as a whole between a metal cathode 1 and a transparent anode 2. The hole transport layer 4 facilitates the infusion of the holes from the anode and blocks electrons. The electron transport layer 5 facilitates the infusion of electrons from the cathode.
In these organic EL devices, a glass substrate 6 is furnished outside the transparent anode 2. The recombination of electrons injected from the metal cathode 1 and the holes injected from the transparent anode 2 to the emitting layer 3 generates excitons. The excitons emit light when they are deactivated through radiation. This light radiates toward outside through the transparent anode 2 and the glass substrate 6.
There have been also known an organic EL device comprising an emitting layer formed of the mixture of an organic fluorescent guest material and an organic host material having a large capability of transporting electrons to stably emit light.
As aforementioned organic EL devices can emit light even by application of a lower voltage, it is firmly expected to develop an EL device capable of emission at a further higher luminance efficiency.